JP2005044878A - Semiconductor device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device provided with both functions of an optical sensor and a memory that can store states. <P>SOLUTION: This semiconductor device has a transistor 9 for the optical sensor and another transistor 10 for comparison formed on a silicon substrate 1. The transistor 9 for optical sensor has a gate oxide film 2a formed on the silicon substrate 1, a gate electrode 3a formed on the oxide film 2a, and source and drain regions 4 and 5 formed in the silicon substrate 1 under the side walls of the gate electrode 3a. The transistor 10 for comparison has a gate oxide film 2b formed on the silicon substrate 1, a gate electrode 3b formed on the oxide film 2b, and source and drain regions 6 and 7 formed in the silicon substrate 1 under the side walls of the gate electrode 3b. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a semiconductor device having both a function as an optical sensor and a memory function capable of storing a state and a manufacturing method thereof.
[0002]
[Prior art]
The optical sensor detects whether or not the light is currently hit. Currently, photodiodes, phototransistors, CdS (cadmium sulphide) cells, and the like are generally used as optical sensors.
In the photodiode, when light is incident, the electrons bonded to the lattice are released to become free electrons, free electrons and holes are generated, and these electrons and holes move to the depletion region. The reverse current has a strength proportional to the intensity of light.
[0003]
The phototransistor is a two-terminal photodetection element having a bipolar transistor structure, and amplifies electron-hole pairs generated by light by a transistor action and detects a photocurrent as a collector current.
The CdS cell is one of II-VI group compound semiconductors and has a wurtzite-type and zinc-blende-type crystal structure and is characterized by large photoconductivity and is mainly used for photoconductive elements.
[0004]
All of the materials listed here operate as an optical sensor using the photovoltaic effect, the photoconductive effect, or the like. Further, the above-described optical sensor counts the amount only when light is applied, and returns to the original state when no light is applied.
[0005]
[Problems to be solved by the invention]
There are many products as optical sensors in semiconductor products. In addition, there are many products that use the devices that can store the state, such as fuses and memory cells, as the characteristics of the product.
However, if you want to have a function that combines both a photosensor and a device that can store data, you have to combine chips as products at the previous stage. If you try to make a single chip, especially in the case of CdS cells, the process becomes complicated And technically difficult.
[0006]
In addition, in order to count the total amount of light hit by the above-described optical sensor, a system for managing by a separate component such as a memory is required in addition to the optical sensor. If it does so, a number of parts will increase, cost will become high, manufacturing will be troublesome, and there exists a possibility that reliability may fall.
[0007]
The present invention has been made in view of the above circumstances, and an object of the present invention is to easily provide a semiconductor device having both a function as an optical sensor and a memory function capable of storing a state, and the semiconductor device at low cost. Another object of the present invention is to provide a method of manufacturing a semiconductor device that can be manufactured easily.
[0008]
[Means for Solving the Problems]
The present invention relates to a semiconductor device having both an optical sensor function and a memory function using a fact that a threshold voltage fluctuates (deteriorates) rapidly when light is irradiated under a certain voltage stress. It is. The degree of light irradiation can be measured by detecting the amount of change in the threshold voltage of the transistor after the semiconductor device is irradiated with light.
[0009]
In order to solve the above problems, a semiconductor device according to the present invention is a semiconductor device having a photosensor transistor and a comparison transistor,
The photosensor transistor includes a first gate insulating film formed on a semiconductor substrate,
A first gate electrode formed on the first gate insulating film;
A first source region and a first drain region formed under the sidewall of the first gate electrode and formed in the semiconductor substrate;
The comparison transistor includes a second gate insulating film formed on the semiconductor substrate;
A second gate electrode formed on the second gate insulating film;
A second source region and a second drain region are formed under the side wall of the second gate electrode and formed in the semiconductor substrate.
[0010]
According to the semiconductor device, the photosensor transistor having the gate electrode, the source and the drain region and the comparison transistor having the gate electrode, the source and the drain region are formed on the semiconductor substrate. In other words, by utilizing the fact that the threshold voltage fluctuates (deteriorates) rapidly when the transistor is exposed to light under a predetermined voltage stress, both the function as an optical sensor and the memory function capable of storing the state are provided on one chip. It is possible to manufacture a semiconductor device prepared for the above.
[0011]
The semiconductor device according to the present invention preferably further includes a circuit for detecting a difference in threshold voltage between the photosensor transistor and the comparison transistor.
[0012]
Further, in the semiconductor device according to the present invention, the circuit applies the voltage stress to the photosensor transistor and applies no voltage stress to the comparison transistor. When the threshold voltage of the photosensor transistor fluctuates by irradiating light, it is also possible to detect a difference between the threshold voltages of the photosensor transistor and the comparison transistor. .
[0013]
A semiconductor device according to the present invention is a semiconductor device including a light receiving portion in which a photosensor transistor and a comparison transistor are arranged in a grid pattern,
The photosensor transistor includes a first gate insulating film formed on a semiconductor substrate,
A first gate electrode formed on the first gate insulating film;
A first source region and a first drain region formed under the sidewall of the first gate electrode and formed in the semiconductor substrate;
The comparison transistor includes a second gate insulating film formed on the semiconductor substrate;
A second gate electrode formed on the second gate insulating film;
A second source region and a second drain region are formed under the side wall of the second gate electrode and formed in the semiconductor substrate.
[0014]
According to the semiconductor device, the light receiving portion in which the photosensor transistor and the comparison transistor are arranged in a lattice shape is formed on the semiconductor substrate. That is, by utilizing the fact that the threshold voltage rapidly fluctuates (deteriorates) when a transistor is exposed to light under a predetermined voltage stress, it can be used as a photographic photosensitive film. Thus, a semiconductor device including both a function as an optical sensor and a memory function capable of storing a state can be manufactured.
[0015]
The semiconductor device according to the present invention may further include a circuit for detecting a difference in threshold voltage between each of the photosensor transistors and the comparison transistors arranged in the lattice shape.
[0016]
Further, in the semiconductor device according to the present invention, the circuit irradiates the light receiving portion with light in a state where voltage stress is applied to each photosensor transistor and voltage stress is not applied to each comparison transistor. Thus, when the threshold voltage of the photosensor transistor fluctuates, a difference in threshold voltage between the photosensor transistor and the comparison transistor is detected, and the difference in threshold voltage is converted into image data. To convert.
[0017]
A method for manufacturing a semiconductor device according to the present invention includes a first gate electrode, a photosensor transistor having a first source region and a first drain region, a second gate electrode, a second source region, and a second source region. A method for manufacturing a semiconductor device comprising a comparative transistor having two drain regions,
Forming first and second gate insulating films on a semiconductor substrate;
Forming a first gate electrode on the first gate insulating film and forming a second gate electrode on the second gate insulating film;
By introducing impurities into the semiconductor substrate using the first and second gate electrodes as a mask, a first source region and a first drain region are formed in the semiconductor substrate under the side wall of the first gate electrode. And forming a second source region and a second drain region in the semiconductor substrate under the side wall of the second gate electrode;
It is characterized by comprising.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(Embodiment 1)
FIG. 1 is a sectional view showing a semiconductor device according to the first embodiment of the present invention.
[0019]
First, gate oxide films 2a and 2b are formed on the surface of the silicon substrate 1 by a thermal oxidation method, and a polysilicon film is deposited on the gate oxide films 2a and 2b by a CVD (chemical vapor deposition) method. Next, by patterning the polysilicon film, gate electrodes 3a and 3b are formed on the silicon substrate 1 via a gate oxide film.
[0020]
Next, by introducing impurities into the silicon substrate in a self-aligning manner using this gate electrode as a mask, source and drain regions 4 to 7 are formed in the silicon substrate 1. Next, an interlayer insulating film 8 made of a silicon oxide film or the like is formed on the entire surface including the gate electrodes 3a and 3b by a CVD method. Next, a resist pattern (not shown) is formed on the interlayer insulating film 8, and the interlayer insulating film 8 is etched using the resist pattern as a mask, whereby a contact hole (not shown) is formed in the interlayer insulating film 8. Provided.
[0021]
Next, a conductive film is deposited in the contact hole and on the interlayer insulating film 8, and this conductive film is patterned to form wiring (not shown). The wiring is electrically connected to the gate electrodes 3a and 3b and the source and drain regions 4 to 7. In this way, the gate electrode 3 a and the source and drain regions 4 and 5 constitute the photosensor transistor 9, and the gate electrode 3 b and the source and drain regions 6 and 7 constitute the comparison transistor 10. The photosensor transistor 9 and the comparison transistor 10 constitute a semiconductor device having both a function as a photosensor and a memory function (function capable of storing a state).
[0022]
In addition, both transistors 9 and 10 before being used as an optical sensor have the same threshold voltage. Each of the photosensor transistor 9 and the comparison transistor 10 is connected to a circuit (not shown) for detecting the difference between the threshold voltages.
[0023]
Next, a method for using the semiconductor device as an optical sensor will be described.
A predetermined voltage stress is applied to the photosensor transistor 9, and no voltage stress is applied to the comparison transistor 10. When light 11 hits both transistors 9 and 10 in this state, the threshold voltage of the photosensor transistor 9 to which voltage stress is applied fluctuates rapidly (deteriorates), but a comparison in which no voltage stress is applied The threshold voltage of the transistor 10 does not change. The amount of change in the threshold voltage varies depending on the degree (irradiation amount) of the light 11 irradiated to the photosensor transistor 9.
[0024]
FIG. 2 is a diagram illustrating an example of a circuit configuration corresponding to the semiconductor device illustrated in FIG.
FIG. 3 is a diagram showing voltage levels of the power supply side line, output 1 and output 2 shown in FIG.
FIG. 4 is a graph showing the relationship between the gate voltage VG and the drain current ID.
[0025]
The photosensor transistor 9 is irradiated with light and the threshold voltage fluctuates as shown in FIG. 4A, and the threshold voltage of the comparison transistor does not change as shown in FIG. 4B. . In this state, the output 1 from the photosensor transistor 9 and the output 2 from the comparison transistor 10 are introduced into a circuit (not shown) for detecting a difference in threshold voltage. At this time, since the threshold voltage of the photosensor transistor 9 fluctuates, the voltage level decreases in the order of the power supply line level, the output 2 level, and the output 1 level as shown in FIG. Then, the threshold voltage difference is derived by comparing the output 1 level with the output 2 level by a circuit for detecting the difference in threshold voltage.
[0026]
Next, the derived threshold voltage difference corresponds to the variation of the threshold voltage of the photosensor transistor 9. By detecting in advance the relationship between the variation in threshold voltage and the amount of light applied to the photosensor transistor 9, the amount of light applied can be detected from the detected variation in threshold voltage. Is possible.
[0027]
According to the first embodiment, the photosensor transistor 9 and the gate electrode 3b including the gate electrode 3a and the source and drain regions 4 and 5, the comparison transistor 10 including the source and drain regions 6 and 7, and the two transistors 9, A circuit (not shown) for detecting the difference between the threshold voltages of the two transistors connected to each of the transistors 10 is formed on the silicon substrate 1. In other words, by utilizing the fact that the threshold voltage fluctuates (deteriorates) rapidly when the transistor is exposed to light under a predetermined voltage stress, both the function as an optical sensor and the memory function capable of storing the state are provided on one chip. Can be manufactured.
[0028]
In addition, since the semiconductor device according to the present embodiment has a simple function and a small number of parts as compared with the conventional optical sensor, manufacturing cost can be reduced, manufacturing effort can be reduced, and reliability can be improved. it can. Further, the threshold voltage fluctuation speed of the photosensor transistor is controlled within a certain range by controlling set values such as the impurity concentration of the channel region of the photosensor transistor 9 and the impurity concentration of the source region and the drain region. be able to.
[0029]
Further, by providing a filter above both transistors 9 and 10, it is possible to control the wavelength of light irradiated to both transistors 9 and 10. Further, there is an advantage that once the threshold voltage of the photosensor transistor 9 is shifted, the state can be maintained without supplying power to the transistor 9.
[0030]
(Embodiment 2)
FIG. 5 is a block diagram schematically showing a semiconductor device according to the second embodiment of the present invention. This semiconductor device has a light receiving portion 12, and this light receiving portion 12 is configured by arranging the photosensor transistors and the comparison transistors shown in FIG. 1 in a grid pattern. That is, a photosensor transistor and a comparison transistor are formed in each lattice portion 12a, and each of the photosensor transistor and the comparison transistor is connected to the circuit 13 by wiring. The circuit 13 detects the shift amount of the threshold voltage Vth of each photosensor transistor by the same method as in the first embodiment.
[0031]
The above-described semiconductor device utilizes a fact that the threshold voltage Vth rapidly fluctuates (deteriorates) when exposed to light under a certain voltage stress, and this is used as a photographic photosensitive film ( This is used as a new image storage method. The threshold voltage Vth of the photosensor transistor changes variously depending on the intensity of light hitting the photosensor transistor. Therefore, the circuit 13 reads the threshold voltage Vth of the photosensor transistor disposed on each grating 12a after the light irradiation, and can convert it into image data. If the amount of light that changes depending on the wavelength of irradiated light is grasped, colorization is possible.
[0032]
FIG. 6 is a diagram in which the semiconductor device shown in FIG. 5 is irradiated with light and the irradiated portion is represented as an image. The circuit 13 detects that light is irradiated to the hatched region (that is, the U-shaped region) 12b and the threshold voltage of the photosensor transistor in the region 12b fluctuates, and the detected optical sensor Diagonal lines are shown in the lattice portion of the transistor.
[0033]
According to the second embodiment, the light receiving unit 12 in which the photosensor transistors and the comparison transistors are arranged in a grid, and the circuit that detects the shift amount of the threshold voltage Vth of the photosensor transistor in each grid portion. 13 are formed on a silicon substrate or in one chip. That is, by utilizing the fact that the threshold voltage rapidly fluctuates (deteriorates) when a transistor is exposed to light under a predetermined voltage stress, it can be used as a photographic photosensitive film. Therefore, a semiconductor device including both a function as an optical sensor and a memory function capable of storing a state can be manufactured in one chip.
[0034]
Further, in the semiconductor device according to the present embodiment, as in the first embodiment, the function is simple and the number of parts is small compared to the conventional optical sensor, so that the manufacturing cost can be suppressed and the manufacturing effort is also reduced. Reliability can also be improved. In addition, the threshold voltage fluctuation speed of the photosensor transistor can be controlled within a certain range by controlling the set values such as the impurity concentration of the channel region of the photosensor transistor and the impurity concentration of the source region and the drain region. Can do.
[0035]
Further, in the present embodiment, as in the first embodiment, it is possible to control the wavelength of light irradiated to both transistors by providing a filter above both transistors. Further, once the threshold voltage of the photosensor transistor is shifted, there is an advantage that an image in that state can be held without supplying power to the transistor.
[0036]
Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, a specific example of the circuit configuration as shown in FIG. 2 is given, but the circuit configuration is not limited to this circuit configuration, and various circuit configurations can be changed depending on the combination of transistors. It is.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a semiconductor device according to a first embodiment.
2 is a diagram illustrating an example of a circuit configuration corresponding to the semiconductor device illustrated in FIG. 1;
3 is a diagram showing voltage levels of a power supply side line, output 1 and output 2 shown in FIG. 2;
FIG. 4 is a graph showing a relationship between a gate voltage VG and a drain current ID.
FIG. 5 is a block diagram schematically showing a semiconductor device according to a second embodiment.
6 is a view showing an irradiation portion as an image by irradiating the semiconductor device of FIG. 5 with light.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2a, 2b ... Gate oxide film, 3a, 3b ... Gate electrode, 4-7 ... Source region and drain region, 8 ... Interlayer insulating film, 9 ... Photosensor transistor, 10 ... Comparison transistor, 11 ... light, 12 ... light receiving part, 12a ... lattice part, 12b ... area with shaded lines (U-shaped area), 13 ... circuit

Claims (7)

A semiconductor device having a photosensor transistor and a comparative transistor,
The photosensor transistor includes a first gate insulating film formed on a semiconductor substrate,
A first gate electrode formed on the first gate insulating film;
A first source region and a first drain region formed under the sidewall of the first gate electrode and formed in the semiconductor substrate;
The comparison transistor includes a second gate insulating film formed on the semiconductor substrate;
A second gate electrode formed on the second gate insulating film;
A semiconductor device having a second source region and a second drain region formed under the side wall of the second gate electrode and formed in the semiconductor substrate. The semiconductor device according to claim 1, further comprising a circuit that detects a difference in threshold voltage between the photosensor transistor and the comparison transistor. The circuit irradiates light to the photosensor transistor and the comparison transistor in a state where voltage stress is applied to the photosensor transistor and no voltage stress is applied to the comparison transistor, thereby the photosensor The semiconductor device according to claim 2, wherein when a threshold voltage of the transistor for use fluctuates, a difference in threshold voltage between the photosensor transistor and the comparison transistor is detected. A semiconductor device including a light receiving portion in which a photosensor transistor and a comparison transistor are arranged in a grid pattern,
The photosensor transistor includes a first gate insulating film formed on a semiconductor substrate,
A first gate electrode formed on the first gate insulating film;
A first source region and a first drain region formed under the sidewall of the first gate electrode and formed in the semiconductor substrate;
The comparison transistor includes a second gate insulating film formed on the semiconductor substrate;
A second gate electrode formed on the second gate insulating film;
A semiconductor device having a second source region and a second drain region formed under the side wall of the second gate electrode and formed in the semiconductor substrate. 5. The semiconductor device according to claim 4, further comprising a circuit that detects a difference in threshold voltage between each of the photosensor transistors and the comparison transistors arranged in the grid pattern. The circuit irradiates light to the light receiving portion in a state where voltage stress is applied to each of the photosensor transistors and no voltage stress is applied to each of the comparison transistors. The threshold voltage difference between the photosensor transistor and the comparison transistor is detected when the value voltage fluctuates, and the threshold voltage difference is converted into image data. Semiconductor device. A photosensor transistor having a first gate electrode, a first source region, and a first drain region, and a comparison transistor having a second gate electrode, a second source region, and a second drain region. A method for manufacturing a semiconductor device comprising:
Forming first and second gate insulating films on a semiconductor substrate;
Forming a first gate electrode on the first gate insulating film and forming a second gate electrode on the second gate insulating film;
By introducing impurities into the semiconductor substrate using the first and second gate electrodes as a mask, a first source region and a first drain region are formed in the semiconductor substrate under the side wall of the first gate electrode. And forming a second source region and a second drain region in the semiconductor substrate under the side wall of the second gate electrode;
A method for manufacturing a semiconductor device, comprising:

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